To monitor the breathing gas composition of a patient, for example, in case of mechanical ventilation, a breathing gas sample is usually taken at the mouthpiece or at the Y-piece of the ventilator or of the ventilation system and this is analyzed by means of gas sensors. Constituents of the breathing gas, such as CO2, oxygen or also anesthetic gases, are typically monitored here continuously. It is important in case of such a continuous monitoring to protect the sensor system (i.e., the gas analysis system) from unintended moisture effects, for example, from water or condensation from the humid breathing air, as well as from biological material, e.g., bacteria, and other contaminants.
WO 2011/103585 A2 proposes in this connection a water trap, which has a filter consisting of a hydrophilic and microporous material. A breathing gas stream can be sent through the water trap. The filter can absorb water of condensation contained in the breathing gas stream and store it. WO 2011/103585 A2 provides, in addition, for an additional hydrophobic filter membrane at the outlet of this device. This filter membrane shall prevent excess liquid from being able to pass through in case of saturation of the hydrophilic filter.
WO 2010/030226 A1 provides for a sample gas line, with which a breathing gas stream can be sent from the patient to a patient gas monitor. This sample gas line is provided with a drying device. This drying device is arranged at the end of the sample gas line directly in front of the patient gas monitor. The breathing gas flowing through the sample gas line is therefore cooled to room temperature level when it reaches the drying device, and excess moisture is removed by condensation. The drying device comprises a moisture-permeable and gas-tight polyether/polyamide block copolymer housing, which is filled with a hydrophilic material.